Ultrasonic welding is used to assembly a top element (e.g. a board, a foil, a base part, a substrate, etc.) to a bottom element (e.g. a board, a foil, a base part, a substrate, etc.) in order to manufacture a microfluidic device, closing then the microfluidic grooves and cavities made on one and/or the other main surface of said first and second elements to form then microfluidic channels and chambers of a microfluidic path. The welding is performed at junction points involving plastic and/or metal materials.
In an industrial environment, ultrasonic welding typically implies the use of energy directors provided on said top or on said bottom elements. Then they are melt for welding purpose by applying simultaneously ultrasonic energy and mechanical pressure for a short time, creating said junction points and the sealing of the top and bottom elements.
It is important that the microfluidics path(s) in the device, usually containing dried or wet reagents or chemistry or coating to be provided during manufacturing of the device, have geometry, dimensions and positions that accurately match with the predetermined design specification of the device, in an industrially reproducible manner. It is in particular key that the welding does not change the design of the microfluidics or does not lead to an inaccuracy due to low tolerances of the welding.
In order to address these requirements, US2009152326 discloses the use of welding stoppers having a certain height and provided on a bottom board, and of energy directors provided on a top board. Once bottom and top boards are assembled in view of the welding for providing the microfluidic device, some gaps separate each energy director from adjacent welding stoppers forming then some welding channels on either side of the energy directors. The melted materials provided from the ultrasonically melting of the tips of the energy directors then flow into these welding channels, and not between the energy directors and the bottom board which would have otherwise created an extra thickness between the two, affecting the weld depth and a good positioning of the bottom and top boards. Furthermore said welding stoppers prevent the top board not to descend anymore when the top and bottom boards are assembled before the welding step, which may further increase the positioning accuracy of the two boards before welding.
Similarly U.S. Pat. No. 6,066,216 discloses the use of welding stoppers and energy directors, separated to each other by welding grooves to receive the melted material, but both welding stoppers and energy directors being provided on the bottom board.